Pub. date: 2010 | Online Pub. Date: December 16, 2009 | DOI: 10.4135/9781412972000 | Print ISBN: 9781412940818 | Online ISBN: 9781412972000| Publisher:SAGE Publications, Inc.About this encyclopedia
Phil Gomersall & David Baguley
The World Health Organisation (WHO), in its factsheet on deafness and hearing impairment, refers to hearing impairment as “the complete or partial loss of the ability to hear from one or both ears. The level of impairment can be mild, moderate, severe or profound.” The classifications are based on hearing thresholds (see Table 1 , next page), most commonly measured using a standard procedure known as pure tone audiometry. In this approach, a measure of the quietest sound an individual can perceive is recorded at a number of different frequencies of sound. Plotting these values creates the audiogram. WHO estimates from 2001 suggest that if an audiogram were to be recorded for every individual on the planet, approximately 600 million people worldwide would have a hearing loss affecting both ears, and 250 million of these would be of moderate-to-profound severity. The actual level of disability resulting from a hearing loss ...